Test against rails4 in travis-ci

- Add gemfile for rails 4.0
- Remove require `active_support/core_ext/float/rounding.rb` if activesupport 4
    - This file is dropped in rails4 (this is patch for ruby1.8)
- Remove errors, add some rails4 features 
     - config.secret_key_base
     - route match
- Add travis-ci config